1. Field of the Invention
This invention relates to an outboard engine in which a flywheel chamber for accommodating a flywheel located below an engine body of an engine is made up of a pump body of an oil pump.
2. Description of the Related Art
There is a known outboard engine in which a flywheel driven by a crankshaft of an engine is disposed under the engine body between its bottom and amount case. For example, in an out board engine disclosed by Japanese Patent Laid-Open Publication No. hei 10-231734, a cylinder block and a crankcase forming the engine body of an engine having a vertically extending crankshaft is united with its coupling portion at a lower end portion thereof to a support portion formed as apart of amount case. The fly wheel provide data lower end portion of the crankshaft is positioned below the engine body, and an oil pump is positioned below it. The flywheel is accommodated in a flywheel chamber made up of the pump body of the oil. pump united to a lower end portion of the engine body, and the coupling portion of the engine body and the support portion of the mount case are united together to surround the pump body from radially outward thereof.
In the prior art technique, a gap in the radial direction is formed in a radial space from the pump body to the coupling portion of the engine body and the support portion of the mount case along the entire circumference. Therefore, the coupling portion and the support portion inevitably increase in outer diameter and weight, and a cover covering the engine and the mount case becomes large. As a result, the outboard engine becomes bulky and heavy.
The present invention has been made under the circumstances, and its main object is to provide a compact, lightweight outboard engine by reducing the size and weight of the connecting portion between the engine body and the mount case that are united together via the pump body of the oil pump. Another object of the invention is to provide an enhanced support strength of the engine body.
According to the invention, there is provided an outboard engine including: an engine having an engine body, a crankshaft extending vertically in the engine body, a flywheel provided on the crankshaft below the engine body, an oil pump driven by a driving power of the crankshaft, and a flywheel chamber defined by a pump body of the oil pump to accommodate the flywheel; and amount case having a support portion for uniting the engine body, characterized in that: the engine body is united with a coupling portion thereof to the support portion via an outer circumferential portion of the pump body such that the coupling portion, the outer circumferential portion of the pump body and the support portion overlap in the direction of extension of a rotating axis of the crankshaft.
According to the invention, since the coupling portion of the engine body, outer circumferential portion of the pump body and support portion of the mount case are united together such that they overlap in the direction of the rotation axis of the crankshaft, it is not necessary to provide the coupling portion and the support portion so as to surround the pump body from radially outward, and outer diameters of the coupling portion and the support portion can be minimized within a range sufficient for the pump body forming the flywheel chamber to accommodate the flywheel.
In addition to that, since the mount case is disposed such that the outer circumferential wall of the pump body overlaps the coupling portion and the support portion in the rotation axis direction, regardless of the coupling portion being united to and supported by the support portion via the pump body, weight of the engine acting upon the outer circumferential portion via the coupling portion is withheld by the support portion of the mount case via the outer circumferential portion, and it is prevented that a bending moment caused by the weight acts on the pump body.
As a result, the following effects are produced. That is, since the engine body is united, with its coupling portion for uniting the pump body defining the flywheel chamber, to the support portion of the mount case via the circumferential portion of the pump body, outer diameters of the coupling portion as the connecting portion between the engine body and the mount case, and of the outer circumferential portion and the support portion, can be minimized and decreased in weight within a range sufficient for the pump body to accommodate the flywheel, and therefore, the outboard engine can be decreased in size and weight. At the same time, since the weight of the engine acting upon the outer circumferential portion of the pump body through the coupling portion is withheld by the support portion of the mount case, it is prevented that a bending moment caused by the weight deforms the pump body. And, since the pump body need not be increased in rigidity to prevent such deformation, this also contributes to decreasing the weight of the pump body and hence the weight of the outboard engine.
The outboard engine may be mounted to a boat stern by a mounting device having a swivel shaft, and the outer circumferential portion may form a circumferential wall of the flywheel chamber. The circumferential wall may have single-wall portions, and a left wall portion and a right wall portion of the circumferential wall may be made of the single-wall portions. Outer diameters of the coupling portion and the support portion in the right and left direction may be substantially equal to the outer diameter of the circumferential wall in the left and right direction as regulated by the left wall portion and the right wall portion.
In this manner, the left wall portion and the right wall portion of the circumferential wall of the flywheel chamber defined by the outer circumferential portion of the pump body are made of singular walls, i.e. single-layered walls in the radial direction of the flywheel, and at the same time, outer diameters of the coupling portion and the support portion in the right and left direction are substantially equal to the outer diameter of the circumferential wall in the right and left direction as defined by the left wall portion and the right wall portion. Therefore, outer diameters of the coupling portion, outer circumferential portion and support portion in the right and left direction can be limited to small values based on minimum values necessary for making the circumferential wall of the flywheel chamber.
As a result, the following effects are produced. That is, since outer diameters of the coupling portion, outer circumferential portion and support portion in the right and left direction can be minimized within a range sufficient for the pump body defining the flywheel chamber to accommodate the flywheel, the cover covering the connecting portion made up of those portions can be decreased in size in the right and left direction, and it is prevented that the outboard engine interferes with other external members in the right and left direction of the connecting portion during right and left rotation of the outboard engine about the swivel shaft. This is effective for increasing the right and left rotatable range of the outboard engine upon steering and for improving the steering efficiency.
The circumferential wall may also include double-wall portions, and a front wall portion and a rear wall portion of the circumferential wall may be made of said double-wall portions. Additionally, outer diameters of the coupling portion and the support portion in the front and rear direction may be substantially equal to the outer diameter of the circumferential wall in the front and rear direction as regulated by the front wall portion and the rear wall portion.
Since the front wall portion and the rear wall portion of the circumferential wall made of the outer circumferential portion of the pump body are made of double-wall portions, i.e. double walls distant in the radial direction of the flywheel, and outer diameters of the coupling portion and the support portion in the front and rear direction are substantially equal to the outer diameter of the circumferential wall in the front and rear direction as regulated by the front wall portion and the rear wall portion, the support strength is enhanced, and the region of the engine body supported by the support portion increases.
As a result, the following effects are produced. That is, the structure configuring the front wall portion and the rear wall portion of the circumferential wall defined by the outer circumferential portion of the pump body to be double-wall portions and substantially equalizing outer diameters of the coupling portion and the support portion in the front and rear direction to the outer diameter of the circumferential wall in the front and rear direction, regardless of the outer diameter of the support portion being small in the right and left direction, the support strength is enhanced, a sufficient support strength of the engine body is ensured, and the region of the engine body supported by the support portion increases. Thus the engine body can be supported more reliably.